On-chip integrated sensors typically require some form of in-situ calibration mechanism that allows the device to separate changes induced by ambient parameters such as temperature and humidity, to name a few, from changes induced in the target parameter being measured. Currently, this is done by integrating secondary temperature and humidity sensing components into the device package as near as possible to the primary sensor in order to measure the ambient parameters that affect the primary sensor's response to the target parameter, for example imposing a DC offset on the normal sensor output signal. While this approach serves to compensate the effect of the ambient or secondary parameters on the sensor output, this practice incurs several disadvantages.
For example, first, in order to correct or calibrate the sensing device readout, signal processing circuity must include a memory having a lookup table to allow for corrections of the sensor readout. This is due to the fact that the secondary sensor structures are non-homologous to the primary sensor structure. An example is the use of thermal diodes or resistors as secondary sensors integrated into an accelerometer package. The correction algorithm executed by a microcontroller or processor must be based on measured primary sensor response behavior under controlled ambient conditions of temperature and humidity, along with calibration curves for the secondary sensors.
Second, the ambient or secondary sensing components often are discrete components, therefore comparatively large, whose incorporation into the package often requires increasing the z-height and form factor of the overall package. Additionally, multiple secondary sensors may be needed to measure multiple ambient parameters, such as temperature and humidity together. As the secondary sensors may be discrete components, there can be some difficulty in collocating the primary sensing device with multiple secondary sensors in close proximity for accurately compensating the effects of the ambient on the primary sensor.